[Theme: Skylark] Move menu under header image

I want to move the menu below the header image on a website I’ve created using Skylark:

http://www.nzbodymechanic.co.nz/

I’ve had a good look around for instructions, but can’t find anything specific to Skylark. Your help would be very much appreciated!

Note I’ve already created a child theme and made some small changes to the style, and have attempted to change the header but it’s not working.